1. Field of the Invention
The present invention relates to a generator of an absorption cooling system. More particularly, the present invention relates to a solution outlet box for the generator.
2. Description of Related Art
Typical absorption chillers have a working solution from which a refrigerant is cyclically vaporized and reabsorbed to provide a cooling effect. Common solutions consist of water and lithium bromide with water being the refrigerant, or ammonia and water, in which case the ammonia is the refrigerant.
In operation, the solution is heated within a generator to vaporize the refrigerant from the solution. For a solution of lithium bromide and water, the water vaporizes, while the remaining solution becomes more concentrated with lithium bromide. For absorption systems using a solution of ammonia and water, the ammonia is the vaporized component.
Vaporizing the refrigerant raises the pressure in the generator. From the generator, the concentrated solution returns to an absorber, while the refrigerant vapor moves into a condenser and condenses there. The liquid refrigerant then enters a lower-pressure evaporator and vaporizes as the refrigerant removes heat from chilled water. The chilled water can then be used as needed, such as to cool rooms or other areas of a building. At the same time, concentrated solution inside the absorber absorbs refrigerant vapor coming from the evaporator and reduces the pressure inside the evaporator to a desired level. Concentrated solution absorbing refrigerant vapor creates a solution of dilute concentration. The dilute solution is then pumped back to the generator to perpetuate the solution separation process.
Properly operating an absorption chiller involves controlling several interrelated variables of the solution. Some of the variables include the temperature, pressure, flow rate, concentration and liquid level of the solution in the generator. Controlling the liquid level in the generator is particularly important, as failure to do so can disrupt absorption chiller operations.
For example, if the liquid level gets too high, violent boiling inside the generator can cause undesirable concentrated solution to be carried over into the condenser and significantly reduce the chiller""s cooling capacity. High liquid levels in the generator may starve the absorber of solution, which may lead to cavitation of the pump that draws solution from the absorber. Excess liquid head in the generator can also cause inefficient vapor generation.
Conversely, if the liquid level in the generator is too low, some heat transfer surfaces may not be submerged, which can possibly damage those surfaces and reduce the chiller""s performance. A prolonged low liquid level can starve a solution outflow pipe that passes concentrated solution from the generator to the absorber and results in losing a liquid seal between the generator and the absorber. Starving the solution outflow pipe of liquid can cause destructive water hammer and/or diminish the effectiveness of a heat exchanger that may be connected in series with the outflow pipe.
Maintaining a proper liquid level in the generator can be difficult, as various operating conditions, may disturb the solution""s liquid level. For instance, if the chiller""s purpose is for cooling a building, a sudden increase in the building""s cooling demand may require the generator to generate more vapor by rapidly boiling more solution. Upon doing so, the level of solution in the generator may drop dramatically. A pump drawing solution from the outlet of the absorber could replenish the generator with more solution; however, as the building""s cooling demand is satisfied, the generator may cool down, and the actual liquid level may overshoot the desired level.
To maintain the liquid level in the generator at a proper level, many devices and control schemes have been developed. One of the more common devices is known as an outlet box. A typical outlet box provides various functions, which may include: providing an outlet for concentrated solution to leave the generator, providing a vapor/liquid seal between a generator and an absorber, and maintaining a proper liquid level in the generator. Various examples of outlet boxes are disclosed in U.S. Pat. Nos. 3,279,212; 4,475,361; 5,381,674 and 5,551,254.
Each of the patents discloses the basic operating function of a particular outlet box; however, the patents discussion of certain control issues, response time in particular, is limited or nonexistent. Failure to address the issue of response time may result in an ineffective outlet box that prevents an absorption chiller from operating at its full potential.
Consequently, a need exists for an absorption apparatus that addresses the issue of response time to avoid control problems such as overshoot, slow response, and hunting.
It is an object of the present invention to balance the flow of solution through an absorption chiller under dramatic cooling load changes by providing the generator with an integrated outlet box that includes a liquid level sensing chamber and a liquid outlet chamber.
Another object of the invention is to maintain a desired liquid level over the generator outlet by controlling the operation of a solution pump system in response to the measurement from a liquid level sensor inside the liquid level sensing chamber. For a quick, consistent indication of the average solution level inside the generator, the liquid level sensing chamber is provided with a liquid opening for passing solution to and from the generator, wherein the liquid opening is sized according to the surface area of the solution inside the liquid level sensing chamber. The sensing chamber also includes a vapor opening that allow vapor to pass between the generator and the level sensing chamber.
To smooth out the boiling effects of the liquid level in the generator, it is an object of some embodiments of the invention to provide the liquid level sensing chamber with a liquid opening whose area is less than the surface area of the solution that is inside the chamber.
To limit the time delay of the liquid level inside the sensing chamber following the liquid level inside the generator, it is also an object to provide the liquid level sensing chamber with a liquid opening whose area is at least a half-percent the surface area of the solution that is inside the sensing chamber.
To further provide a good measurement of the liquid level in the generator, it is an object of the invention to provide the liquid level sensing chamber with a liquid opening whose area is between ten to fifty percent of the area of the liquid surface area of the solution that is inside the chamber.
Another object of the invention is to divide the integrated outlet box with a common dividing wall that is shared by the liquid level sensing chamber and the liquid outlet chamber.
Another object is to provide the common dividing wall with a hole that is open to the liquid level sensing chamber and the liquid outlet chamber at their bottoms. The liquid level in the level sensing chamber can then be measured to predict the liquid solution level changes in the generator for better solution flow control when the chiller is under dramatic cooling load changes. If the absorption chiller is not running, the hole will allow the concentrated solution in the level sensing chamber to drain.
Yet, another object of the invention is size the hole in the common dividing wall so that it is no more than a fourth the size of the surface area of the solution that is inside the liquid level sensing chamber. This helps minimize adverse effects of flow through the hole when the solution""s liquid level is above the liquid opening in the liquid level sensing chamber.
Yet still another object is to provide an outlet box that helps keep the liquid level in the outlet chamber near the liquid level in the generator when the chiller is running. To do this, the liquid outlet chamber is provided with a relatively large opening into the generator, wherein the opening is larger than the liquid opening in the liquid level sensing chamber.
A further object is to have the opening in the liquid outlet chamber be larger than the hole in the common dividing wall to help maintain a relatively calm liquid surface in the liquid level sensing chamber.
A still further object is provide the liquid opening of the liquid level sensing chamber with a width greater than its height to help distribute the opening over a uniform elevation.
Another object of the invention is to keep the liquid opening of the liquid level sensing chamber relatively close to the opening in the liquid outlet chamber, so that the liquid level in the liquid level sensing chamber responds closely to amount of solution flowing into the outlet chamber.
Another object is to use the integrated outlet box to maintain a liquid seal between the generator and an absorber, thus helping to ensure that a solution-to-solution heat exchanger is kept flooded with liquid solution.
Another object is to use the integrated outlet box to safeguard the minimum liquid level inside the generator by aligning all openings for passing liquid solution to the required minimum liquid solution level of the generator. If the chiller is running and the liquid level in the level sensing chamber is lower than the minimum required level, the level sensor will inform the unit controller to take appropriate actions.
Another object is to use the integrated outlet box to safeguard the maximum liquid level inside the generator by aligning all openings for passing vapor higher than the required maximum liquid solution level of the generator. If the chiller is running and the liquid level in the level sensing chamber is higher than the maximum required level, the level sensor will inform the unit controller to take appropriate actions.
Another object is to provide the integrated outlet box with a deflector plate that helps block the solution flowing upward along the side of the generator. Blocking such flow provides for better correlation between the liquid level in the level sensing chamber and the solution outflow from the generator.
Another object is have screens cover all openings between the generator and the integrated outlet box to protect the heat exchanger on the return line and to improve the vapor-liquid separation in the outlet chamber.
These and other objects of the invention are provided by an absorption apparatus that includes a generator in fluid communication with a liquid level sensing chamber and a liquid outlet chamber. The liquid sensing chamber is provided with an opening into the generator, with the opening being sized according to the liquid surface area of the solution that is inside the liquid level sensing chamber. The liquid outlet chamber is provided with a significantly larger opening into the generator. The larger opening provides a more open flow path for solution to exit the generator through the liquid outlet chamber. The more restricted opening in the liquid level sensing chamber allows a liquid level sensor therein to sense a relatively calm liquid level that tends to be at an average elevation of a boiling-disrupted liquid level in the generator. With the opening in the liquid level sensing chamber being appropriately sized, a solution pump system controlled in response to the liquid level sensor can effectively maintain a desired solution liquid level in the generator under a wide range of chiller operating conditions.